Several houses being used for cannabis growing operations were shut down in Auckland today, after police uncovered a large-scale drug syndicate operating between New Zealand and Canada.

Operation Express began in December 2012 involving staff from the Organised Financial Crime Agency New Zealand, police and customs working with the Royal Canadian Mounted Police and other agencies across the Pacific region.

Five search warrants were executed in Auckland today with further warrants executed in Vancouver.

The raids follow the execution of 14 warrants in Auckland last week where five fully-operational grow houses were located and 10 people were arrested.

Those arrested last week are Vietnamese - 7 male and 3 female - aged between 18 and 34.

The investigation began after Canadian authorities seized two separate shipments of methamphetamine totalling 6.6kg in December 2012. This was concealed in a consignment of truck shock absorbers and destined for New Zealand, with an estimated street value of $7 million.

The joint investigation also established the syndicate was involved in the large scale cultivation of cannabis in a number of houses allegedly rented for that purpose, mainly on the North Shore.

More than 600 fully developed cannabis plants were seized in last week's operation together with an ounce of methamphetamine and about $90,000 in cash.

Two of those arrested last week are now also charged with conspiracy to import and importing methamphetamine. A further person has been arrested today and also charged in respect to the two failed importations seized in Canada and an additional three previous importations into New Zealand.

In total 11 people have been arrested - one a patched gang member.

Detective Inspector Bruce Good said the trans-Pacific operation was a great success but he was stunned by the risks people had taken in cultivating the drug.

"We've been dealing with live wires hanging loose, connections to the mains supply by-passed and houses left without any earthing mechanism. This type of tampering is potentially life threatening through the risk of either electric shock or fire"

"I urge all landlords to do regular, thorough checks on their properties to reduce such a risk," said Good.